Aqueous Model Systems Research Articles

Construction and Application of a Static Magnetic Field Exposure Apparatus for Biological Research in Aqueous Model Systems and Cell Culture.

With the growth of the quantum biology field, the study of magnetic field (MF) effects on biological processes and their potential therapeutic applications has attracted much attention. However, most biologists lack the experience needed to construct an MF exposure apparatus on their own, no consensus standard exists for exposure methods, and protocols for model organisms are sorely lacking. We aim to provide those interested in entering the field with the ability to investigate static MF effects in their own research. This protocol covers how to design, build, calibrate, and operate a static MF exposure chamber (MagShield apparatus), with instructions on how to modify parameters to other specific needs. The MagShield apparatus is constructed of mu-metal (which blocks external MFs), allowing for the generation of experimentally controlled MFs via 3-axial Helmholtz coils. Precise manipulation of static field strengths across a physiologically relevant range is possible: nT hypomagnetic fields, μT to < 1 mT weak MFs, and moderate MFs of several mT. An integrated mu-metal partition enables different control and experimental field strengths to run simultaneously. We demonstrate (with example results) how to use the MagShield apparatus with Xenopus, planarians, and fibroblast/fibrosarcoma cell lines, discussing the modifications needed for cell culture systems; however, the apparatus is easily adaptable to zebrafish, C. elegans, and 3D organoids. The operational methodology provided ensures uniform and reproducible results, affording the means for rigorous examination of static MF effects. Thus, this protocol is a valuable resource for investigators seeking to explore the intricate interplay between MFs and living organisms. Key features • A comprehensive roadmap, suitable for undergraduate to advanced researchers, to construct an apparatus for in vitro and in vivo experiments within uniform static magnetic fields. • Designed to fit inside standard incubators to accommodate specific environmental conditions, such as with cell culture, in addition to stand-alone operation at room temperature. • Requires two DC power supplies and 3D printer access for the Helmholtz coils, Plexiglass and mu-metal foil for the partition, and a milli/Gaussmeter for calibration. • Requires ordering a custom mu-metal shell from a commercial resource (using provided schematics), where lead times for delivery can vary from 2 to 4 months.

Scanning Gas Diffusion Electrode Setup for Real-Time Analysis of Catalyst Layers.

The scanning gas diffusion electrode (S-GDE) half-cell is introduced as a new tool to improve the evaluation of electrodes used in electrochemical energy conversion technologies. It allows both fast screening and fundamental studies of real catalyst layers by applying coupled mass spectrometry techniques such as inductively coupled plasma mass spectrometry and online gas mass spectrometry. Hence, the proposed setup overcomes the limitations of aqueous model systems and full cell-level studies, bridging the gap between the two approaches. In this proof-of-concept work, standard fuel cell electrodes are investigated at elevated oxygen reduction reaction current densities, while dissolved Pt x+ ions in the electrolyte and gaseous CO2 in the outlet gas stream are detected to track platinum dissolution and carbon corrosion, respectively. Relevant current densities of up to 0.75 A cm-2 are demonstrated. The electrochemically active surface area, oxygen reduction reaction activity, and Pt dissolution rates are quantified and benchmarked to the values obtained in the conventional stationary GDE half-cell. Moreover, it is found that Pt dissolution is suppressed when O2 is purged into the catalyst layer. Overall, this work demonstrates the feasibility of fast fuel cell electrode screening obtaining, complementary to electrochemical, mass spectrometry data necessary in fundamental studies on structure/performance relationships under actual reaction conditions. While Pt/C, in relevance to its fuel cell application, is used in this study, the proposed setup can be applied in water electrolysis, CO2 conversion, metal-air batteries, and other neighbor technologies.

Molecular interactions by thermodynamic and computational molecular docking simulations of selected strawberry esters and pea protein isolate in an aqueous model system

The objective of this study was to determine the interactions between selected strawberry esters and pea protein isolate (PPI) in a protein-containing aqueous model system, utilizing modified ultrafiltration and equilibrium dialysis techniques. Strawberry esters, including ethyl butanoate, ethyl isopentanoate, ethyl hexanoate, and methyl anthranilate, demonstrated different binding parameters to the PPI. Overall flavor binding affinities (nK) of all esters decreased as the temperature increased from 5 °C to 25 °C. Among these compounds, ethyl hexanoate exhibited the highest affinity to PPI at 25 °C. Thermodynamic parameters revealed that all ester-PPI interactions were spontaneous and enthalpy-driven, primarily involving van der Waals forces or hydrogen bonding. In addition, computational molecular docking studies also identified alkyl hydrophobic interactions in ester-PPI complexes. These findings illustrated that understanding the interactions between esters and PPIs can assist in determining the optimal proportions of compounds for flavorings in high-protein beverages from pea protein.

A rapid method to quantify sub-micrometer polystyrene particles in aqueous model systems by TOC analysis

For several laboratory experiments with microplastics, a simple and fast quantification method is advantageous. At the same time, the requirements are often lower compared to microplastic detection from environmental samples. We determined the concentration of non-purgable organic carbon of polystyrene (PS) particles (diameter 0.5, 1, 2, 6 μm) in suspension with known concentrations. Commercially available PS particles were used to test the Total Organic Carbon (TOC) analyzer method for quantifying microplastics in the lower micrometer range under absence of other organic compounds. Addition of iron or aluminum hydroxide to the samples prior to the measurement increased the recovery from 52.9 to 89.7% relative to measurements in the absence of metal hydroxides. With increasing particle size, the recovery in the presence of iron hydroxides decreased from 95.1% at 0.5 μm to 67.1% at 6 μm PS particles and in the presence of aluminum hydroxides from 92.6% at 0.5 μm to 88.9% at 6 μm PS particles. We conclude that metal hydroxides have a catalytic effect on the thermocatalytic oxidation of PS particles and allow a complete conversion to CO2 for a successful quantification of PS particles using a TOC analyzer. Especially for particles larger than 0.5 μm, in the absence of metal hydroxides, the TOC device is not able to fully oxidize the PS particle to CO2 and subsequently detect its concentration. Thus, TOC analysis of PS particles in the presence of metal hydroxides provides a cheap and simple alternative for quantifying microplastic particles in the lower micrometer range for laboratory experiments (e.g. sedimentation studies) where no other organic substances are present.

Benchmarking Stability of Iridium Oxide in Acidic Media under Oxygen Evolution Conditions: A Review: Part II

Part I () introduced state-of-the-art proton exchange membrane (PEM) electrolysers with iridium-based catalysts for oxygen evolution at the anode in green hydrogen applications. Aqueous model systems and full cell testing were discussed along with proton exchange membrane water electrolyser (PEMWE) catalyst degradation mechanisms, types of iridium oxide, mechanisms of iridium dissolution and stability studies. In Part II, we highlight considerations and best practices for the investigation of activity and stability of oxygen evolution catalysts via short term testing.

Accelerating Real-Time Analysis of Gas Diffusion Electrodes Using Different Coupled Mass Spectrometry Techniques

Due to the rapid development of new catalysts, simple electrochemical screening methods are needed to evaluate the activity and stability of catalyst layers. Setups for these applications already exist: the so-called Scanning Flow Cells (SFCs) unify real-time electrochemical activity and dissolution stability analysis in a high-throughput fashion and find applications in a broad range of topics, such as battery research, 1 oxygen evolution reaction catalysts performance,2 and photo-electrochemistry.3 Yet, the low current densities reached in the system hinder the direct comparison of the results to real devices.4 Gas diffusion electrode (GDE) based setups present a promising alternative to Aqueous Model Systems (AMS) due to their ability to achieve higher current densities. Compared to two electrode full cells (fuel cell or water electrolyser), GDE half-cells are operated in a three-electrode configuration with liquid electrolyte. However, as in fuel cells, gasses reach the catalyst layer through a flow field, achieving relevant current densities up to 2 A cm-2. The GDE half- cell offers the advantage of studying the isolated reaction of the working electrode by applying controlled potentials with a reference electrode. While the GDE offers a simplified approach, the assembly process can be time-consuming, and the overall catalyst throughput analysis could be further optimised.5,6 In this context, we present a novel setup that enables the rapid examination of catalyst layers for fuel cells, providing more realistic conditions while simultaneously investigating degradation processes. The setup consists of an optimised SFC based on lower internal resistance and an additional flow field to purge the catalyst layer with different gasses. As the common SFC, the presented Scanning Gas Diffusion Electrode half cell (S-GDE) can be connected to an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) to quantify the dissolution of metals in real-time. Furthermore, the gas-sensitive Mass Spectrometer can be connected to the gas stream of the cell, enabling the detection of volatile products via on-line electrochemical mass spectrometry (OLEMS). The simple replacement of catalyst layers in the S-GDE allows fast analysis of multiple catalysts consecutively. Still, as the aim is to facilitate high-throughput electrochemistry, developing the S-GDE is ongoing. Furthermore, the optimised cell can reach higher current densities than cells of a similar design, allowing accelerated stress tests (ASTs) and the performance of polarisation curves.The S-GDE will offer a new perspective on realistic catalyst layers, their performance, and catalyst/support degradation processes, e.g. Pt dissolution and carbon corrosion. The increasing demand for new catalyst materials highlights the need for their rapid evaluation under realistic conditions, taking into account not only their electrochemical performance but also their stability. Lüchtefeld J, Hemmelmann H, Wachs S, Mayrhofer KJ, Elm MT, Berkes BB. Effect of Water Contamination on the Transition Metal Dissolution in Water-Enriched Electrolyte: A Mechanistic Insight into a New Type of Dissolution. The Journal of Physical Chemistry C. 2022;126(40):17204–11.Zlatar M, Nater D, Escalera-López D, Joy RM, Pobedinskas P, Haenen K, et Evaluating the stability of Ir single atom and Ru atomic cluster oxygen evolution reaction electrocatalysts. Electrochimica Acta. 2023;444:141982.Jenewein KJ, Kormányos A, Knöppel J, Mayrhofer KJJ, Cherevko S. Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS Measurement Science Au. 2021;1(2):74–81.Ehelebe K, Escalera-López D, Cherevko S. Limitations of aqueous model systems in the stability assessment of electrocatalysts for oxygen reactions in fuel cell and Current Opinion in Electrochemistry. 2021;29:100832.Ehelebe K, Knöppel J, Bierling M, Mayerhöfer B, Böhm T, Kulyk N, et Platinum Dissolution in Realistic Fuel Cell Catalyst Layers. Angewandte Chemie (International ed in English). 2021;60(16):8882–8.Ehelebe K, Seeberger D, Paul MTY, Thiele S, Mayrhofer KJJ, Cherevko S. Evaluating Electrocatalysts at Relevant Currents in a Half-Cell: The Impact of Pt Loading on Oxygen Reduction Reaction. Journal of The Electrochemical Society. 2019;166(16):F1259-F68. Figure 1: The S-GDE unifies the real conditions approach of the GDE and the high throughput approach of the SFC and the connection to two mass spectrometer enables the real time detection of dissolved catalyst (ICP-MS) and volatile products (OLEMS). Figure 1

Unveiling the Impact of Carbon Corrosion on the Degradation of Fe-N-C Catalyst Layers in Alkaline Media

One of the most promising candidates to replace platinum group metal catalysts for oxygen reduction reaction (ORR) in fuel cells (FCs) is the sub-class of iron-nitrogen-carbon (Fe-N-C) catalysts. However, Fe-N-C materials considerably suffer from varied degradation mechanisms. [1-2] Compared to FC operating conditions, start/stop events where the cathodes experience anodic potential may be more damaging due to the carbon corrosion phenomenon. [3] The correlation between carbon corrosion and Fe dissolution rates has been reported in aqueous model systems in acidic media. [3] However, different carbon corrosion mechanisms are reported for acidic and alkaline media. [4] While anion-exchange membrane FCs (AEMFCs) have gained increased attention, studies on the effects of carbon corrosion on realistic AEMFC Fe-N-C catalyst layers are still missing.In this work, using a gas diffusion electrode (GDE) half-cell coupled with inductively coupled plasma mass spectrometry (ICP-MS), [5] we observed that the rate of Fe loss significantly accelerates with rising potential (E > 1.0 VRHE), commonly experienced during the start/stop events. Increased temperature intensifies the rate of Fe leaching during carbon corrosion (see Figure 1), while the gas atmosphere (Ar or O2) shows a negligible influence. On the contrary, the subsequent Fe deposition and the drop of ORR activity depend on the presence of O2 and the varied temperature. Combining in situ and post-mortem analyses, we report how carbon corrosion in alkaline media degrades Fe-N-C catalyst layers in various atmospheres and at different temperatures. These insights can contribute to rational designs of AEMFCs' start/stop protocol and more robust Fe-N-C materials. Figure 1. Fe-N-C demetallation during anodic potential holds (1.0 - 1.5 VRHE) in O2-saturated alkaline (0.1 M NaOH) environment at 22 ± 2 and 62 ± 2 ℃. (A) Potential profile. (B) The Fe dissolution rate normalized to catalyst loading.

Oxidative stability differences of aqueous model systems of photoautotrophic n–3 LC–PUFA rich microalgae: The antioxidative role of endogenous carotenoids

Microalgae rich in omega-3 long-chain polyunsaturated fatty acids (n–3LC–PUFA) have already shown their potential for developing functional food rich in these healthy fatty acids. Not only could they offer a more sustainable alternative for the fish stock that is currently relied upon but is unable to keep up with the demand, enrichment with certain microalgae also leads to oxidatively stable products. Although the reason for this stability has been attributed to the presence of endogenous carotenoids, further insight into their antioxidative role is missing and would be clarifying for selecting the proper microalgae for food enrichment. In trying to further accomplish this, a storage experiment (4 weeks, 37 °C) was set up with the parallel analysis of both oxidation products (primary and secondary) and carotenoids of two aqueous model systems of different (promising) microalgae (Nannochloropsis and Phaeodactylum). The results showed a clear difference in oxidative stability despite both microalgae containing endogenous carotenoids: Nannochloropsis led to oxidatively unstable and Phaeodactylum to oxidatively stable products. This was clearly confirmed by the analysis of n–3LC–PUFA throughout storage which showed a breakdown of half of the n–3LC–PUFA for Nannochloropsis. All carotenoids (violaxanthin, zeaxanthin and β-carotene for Nannochloropsis, and fucoxanthin and β-carotene for Phaeodactylum) acted as an antioxidant as shown by their degradation throughout storage, but the difference in oxidative stability pointed out an impact of carotenoid content and (possibly) type. The presence of a sufficient amount of carotenoids seems to be an important factor for perceiving oxidative stability. Phaeodactylum has shown to be more potent for food enrichment.

Presence of free gallic acid and gallate moieties reduces auto-oxidative browning of epicatechin (EC) and epicatechin gallate (ECg)

Auto-oxidation of flavan-3-ols leads to browning and consequently loss of product quality during storage of ready-to-drink (RTD) green tea. The mechanisms and products of auto-oxidation of galloylated catechins, the major flavan-3-ols in green tea, are still largely unknown. Therefore, we investigated auto-oxidation of epicatechin gallate (ECg) in aqueous model systems. Oxidation products tentatively identified based on MS included δ- or γ-type dehydrodicatechins (DhC2s) as the main contributors to browning. Additionally, various colourless products were detected, including epicatechin (EC) and gallic acid (GA) from degalloylation, ether-linked ε-type DhC2s, and 6 new coupling products of ECg and GA possessing a lactone interflavanic linkage. Supported by density function theory (DFT) calculations, we provide a mechanistic explanation on how presence of gallate moieties (D-ring) and GA affect the reaction pathway. Overall, presence of gallate moieties and GA resulted in a different product profile and less intense auto-oxidative browning of ECg compared to EC.

Comparison of the Thermal and Rheological Properties of Frontière Brown Rice Flour, Tapioca Starch, and Potato Starch and Mixture Effects on Pasting Properties in Aqueous Systems

AbstractGluten‐free blends utilize starches, gums, hydrocolloids, and proteins for viscoelasticity, gas holding ability, and crumb structure of dough and batter without gluten. This study examines Frontière brown rice flour (HPBRF), a new high protein rice cultivar, with tapioca starch (TS) and potato starch (PS) in an aqueous model system in a mixture design, to study interaction effects on pasting properties. The effect of the flour from this new cultivar on the pasting properties of other starches typically used in gluten‐free products has not yet been tested. Pasting properties are analyzed with a Rapid Visco Analyzer (RVA). Rheological and thermal characterization of the flour and starches are also done using differential scanning calorimetry (DSC) and a rheometer. The blends of HPBRF and PS affect the pasting properties compared to each alone, and it is observed that the application of HPBRF with PS decreases breakdown viscosity and peak viscosity, significantly compared to PS alone. Also, the ternary mixture considerably decreases the retrogradation potential for HPBRF, which indicates more stability during storage. These positive and negative effects can indicate how combined usage of these ingredients for the development of bakery products can impact physiochemical properties of gluten‐free bakery products.

Structural and Functional Characteristics of Hemp Protein Isolate–Pullulan Polysaccharide Glycosylation Conjugate in an Aqueous Model System

Hemp protein, with its important nutritional and industrial value, has trickled into the aisles of protein demand; however, its poor functional properties have largely limited its implementation in food. Herein, we aimed to modify hemp protein isolate (HPI) via glycosylation coupling with pullulan polysaccharide, and we subsequently characterized its structural and functional properties. The conjugation variables were HPI to pullulan ratio (i.e., 3:1, 2:1, 1:1, 1:2, and 1:3 w/w), incubation temperature (i.e., 50, 60, 70, 80, and 90 °C), and incubation time (i.e., 3, 6, 12, 24, and 48 h). Native HPI was used as a control for comparison purposes. We found that DG tended to decrease when the pullulan to HPI ratio was greater than 1:1 and when the temperature exceeded 80 °C. SDS-PAGE analysis shows that when the DG is increased, wider and heavier molecular weight bands emerge near the top of the running gel, while such observations were absent in the control. Further, glycosylation could loosen the HPI's secondary and tertiary structures, as well as increase surface hydrophobicity. The solubility of HPI after glycosylation significantly increased (p < 0.05) at pH 7.0 compared to HPI without glycosylation. Emulsifying activity improved significantly (p < 0.05), with glycosylation with HPI-pullulan at a ratio of 1:3 showing maximum emulsifying activity of 118.78 ± 4.48 m2/g (HPI alone: 32.38 ± 3.65 m2/g). Moreover, the HPI-pullulan glycosylation time of 24 h showed maximum foaming activity (23.04 ± 0.95%) compared to HPI alone (14.20 ± 1.23%). The foaming stability of HPI (79.61 ± 3.33%) increased to 97.78 ± 3.85% when HPI-pullulan was conjugated using a glycosylation temperature of 80 °C. Compared with the un-glycated HPI, HPI-pullulan also increased WHC (4.41 ± 0.73 versus 9.59 ± 0.36 g/g) and OHC (8.48 ± 0.51 versus 13.73 ± 0.59 g/g). Intriguingly, correlation analysis showed that protein functional characteristics were significantly and positively correlated with DG. Overall, our findings support the notion that pullulan conjugation provides further functional attributes to the HPI, thereby broadening its potential implementation in complicated food systems.

Formation of furanoic compounds in model systems with saccharides, amino acids, and fatty acids, analyzed with headspace-solid phase micro-extraction-gas chromatography–tandem mass spectrometry

Furan and furan derivatives are processing contaminants found in thermally processed food, such as coffee or canned products. For the determination of furan and ten derivatives, a sensitive headspace-solid phase micro-extraction-gas chromatography–tandem mass spectrometry method with stable isotope dilution analysis was developed. Different precursors such as saccharides, saccharide/amino acid mixtures, polyunsaturated fatty acids (PUFA), and oils were heat processed to investigate the formation of furanoic compounds via Maillard reaction and lipid oxidation. Therefore, a low moister (silica gel with 10% water content) and an aqueous (phosphate buffer, pH 4.5, 7, and 9) model system were chosen to study the effect of water content and pH value on the formation process. The formation of different furan derivatives could be attributed to distinct precursors; furfuryl alcohol was highly formed from 1,4-linked disaccharides, whereas PUFA formed the highest amounts of 2-ethylfuran and 2-pentylfuran.

Effect of pH on Electrochemical Dissolution of Iridium

Replacing fossil fuels with renewable energy sources is one of the most challenging tasks in today's society. As renewable sources are intermittent in nature, a promising solution is to store the produced energy in the form of hydrogen, which can be produced electrochemically by using proton exchange membrane water electrolyzers (PEMWEs). A limiting factor of PEMWEs is that the harsh conditions and sluggish kinetics of oxygen evolution reaction (OER) at the PEMWE anode require that the state-of-the-art catalysts employed are based mostly on Iridium (Ir). (1) Given its scarcity, the use of Ir in OER electrocatalysis is under increasing scrutiny, where current efforts have focused on maximizing activity while decreasing its loading. This is crucial in order to implement PEMWEs in the giga-to-terawatt scale, one of the goals set by the U.S. DoE "Hydrogen Shot". (2)The benchmarking of Ir catalysts for OER electrocatalysis is mostly performed in aqueous model systems (AMS) using acidic electrolytes, but recent works directly comparing AMS and PEMWE showed a clear discrepancy in the catalyst lifetimes. (3) Indeed, a higher pH value under PEMWE operation (ca. 3) was proposed as the main factor responsible for the extended lifetimes. (4) Consequently, both activity and stability of Ir need to be carefully reassessed in a wider pH window. Several works have already evaluated the influence of pH on Ir OER activity over the entire pH scale with buffered (5) and unbuffered electrolytes, (6) but so far, very few works have looked into its stability. Ir stabilities have been reported either in highly acidic (1) or alkaline conditions, (7) where Ir stability significantly changed between such pHs. In this context, studying the Iridium stability over the entire pH scale is essential for understanding and designing more stable and active catalysts.The presented work aims to fill the gap in the current literature regarding Ir activity-stability relationships at different pHs. To do so, we tested a polycrystalline iridium electrode with scanning flow cell coupled to an inductively coupled plasma mass spectrometer setup (SFC-ICP-MS) in pH range from 1 to 12.7. For pH 1 and 12.7, 0.1 M HClO4 and 0.05 M KOH were used, respectively, while pH range of 3-11 was achieved by the addition of phosphate buffer. Using this approach, we distinguished the clear influence of pH on the stability of Iridium, which decreased by shifting the pH value from 1 to 12.7. Lastly, the lower stability of Ir in near-neutral pH compared to acidic, raises questions about the applicability of OER at near-neutral pHs in buffered conditions, which recently gained increased attention.

Binding of dual‐flavour compounds by soy protein isolate in aqueous model systems

SummaryBy the technique of headspace solid‐phase microextraction/gas chromatography–mass spectrometry (SPME‐GC/MS) and static headspace/gas chromatography (HS/GC), the interaction of dual‐flavours and soy protein isolates (SPI) was determinated at low flavour concentration (0.04–0.16 mm) and high flavour concentration (0.4–1.6 mm). The results show that the mixture of ethyl caprylate and undecanal that has elongated structure possesses the same binding sites on SPI and shows competitive binding; the mixture of carvone that has compact structure, at low flavour concentration, possesses different and independent binding sites on SPI, and there maybe existed noncompetitive binding. If high concentration multi‐flavour binding with SPI induces the conformational change and increased more binding sites for another single flavour, there may be existed anticompetitive binding. ‘Salt out’ effects of interaction model were observed for terpene flavours.

The Interplay of Oxygen Reduction Reaction and Iron Dissolution from Fe-N-C Electrocatalysts

Fe-N-C catalysts are regularly proposed as promising earth-abundant and cheap catalysts replacing platinum group metal catalysts for fuel cells (FCs). Besides the activity, especially the stability of those materials remains challenging. It was found that the electrochemical activity and durability of Fe-N-C catalysts are superior in alkaline compared to acidic media, [1-3] yet most of their degradation studies are done in acidic media. [4-9] Moreover, although these are systematic works, discrepancies in these results from aqueous model systems (AMS) [5,6] and FC testing [7-9] remain puzzling. For example, the origin of the dissolved Fe species was found to be from poorly active sites in AMS [5] yet from highly active sites in operating FCs. [7,8] Additionally, the harmful effects of reactive oxygen species (ROS) on Fe-N-C catalysts are proven in AMS [6] but not directly correlated to the durability in FCs. [9] To bridge this gap, a gas diffusion electrode (GDE) half-cell coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been developed to study on-line dissolution in realistic catalyst layers. [10] In this work, using a GDE-ICP-MS, we investigate the impacts of oxygen reduction reaction (ORR) on Fe leaching from realistic Fe-N-C alkaline catalyst layers. [11] For the first time, Fe dissolution is measured online at current densities above -100 mA·cm-2. The novel results show that compared to the model Ar-saturated environment, the Fe dissolution is dramatically higher during ORR. Furthermore, between 0.6 and 1.0 VRHE, we unveil an interesting correlation between Fe dissolution and charge transfer events. This subsequently leads to our hypothesis that the instability of the coordinated Fe during Fe3+/Fe2+ redox transitions is responsible for Fe leaching from Fe-N-C catalysts in alkaline media in this potential region. The novel insights into Fe-N-C catalyst degradation in realistic conditions can lead to rational design of this promising platinum group metal free catalyst for efficient, durable, and affordable FCs.

Catalyst Dissolution Analysis in PEM Water Electrolyzers during Intermittent Operation

Sustainable development of the global energy sector requires a transition from fossil fuels to renewable energies. Considering the continuously increasing energy demand, effective utilization of intermittent output from the renewable sources will depend on the efficiency of energy storage and utilization processes. Low chemical complexity and high energy density and efficiency make hydrogen produced via proton exchange membrane water electrolysis (PEMWE) a prominent solution for the mentioned challenges.Acidic conditions and high potentials at the anode side of PEM water electrolyzers, where the oxygen evolution reaction (OER) takes place, demand for materials with high catalytic activity and corrosion stability. The state-of-the-art platinum and iridium (oxide) catalysts in the cathode and anode catalyst layers (CLs), respectively, demonstrate relatively good activity and stability during steady operation at low and moderate electrical loads. Indeed, it is anticipated that a significant decrease in the noble metal amount may be achieved without sacrificing the cell performance [1]. An intermittent operation of PEMWE, however, represents a considerable risk factor as both CLs may degrade with time. The extent of such degradation, especially at low catalyst loadings and high current densities, alternated with numerous off cycles is still not well understood and hence, difficult to predict and mitigate.Recent results from our group indicate a severe discrepancy between OER catalyst dissolution in aqueous model systems (AMS) and membrane electrode assemblies (MEA), with the main reasons being a suggested discrepancy between estimated and real pH in MEA and stabilization occurring over time [2]. In this work, CLs degradation during dynamic electrolyzer operation in a specially designed PEMWE test station was studied via ex-situ inductively coupled mass spectrometry analysis (ICP-MS) and its influence on the cell’s overall performance was analyzed. The S number, a new metric for OER catalyst lifetime estimation [3], was also used to compare catalyst stability properties within the two systems.

Photo-Oxidative Stability of Aqueous Model Systems Enriched with Omega-3 Long-Chain Polyunsaturated Fatty Acid-Rich Microalgae as Compared to Autoxidative Stability.

Several species of microalgae are promising as an alternative source of omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). Photoautotrophic species show the greatest potential, since incorporating them into food products leads to oxidatively stable products; however, the presence of photosensitizers could reduce the shelf-life due to the appearance of photo-oxidation on exposure to light. This study investigated the oxidative impact of illumination for aqueous model suspensions enriched with Phaeodactylum (phototrophic microalgae─containing potential photosensitizers) and Schizochytrium (heterotrophic microalgae─lacking photosensitizers) during storage for 28 days at 37 °C. Primary (peroxide value) and secondary (volatiles with gas chromatography (GC)-mass spectrometry) oxidation products, n-3 LC-PUFA content (GC), and pigments (high-pressure liquid chromatography) were assessed. The results showed that photo-oxidation did not cause oxidative instability for Phaeodactylum samples compared with strong autoxidation in Schizochytrium samples. For the Phaeodactylum-enriched suspensions, only minimal photo-oxidation could be detected and the n-3 LC-PUFA content remained stable throughout storage regardless of illumination.

Limitations of aqueous model systems in the stability assessment of electrocatalysts for oxygen reactions in fuel cell and electrolyzers

Cost and stability remain the greatest technical barriers to sustainably commercialize low-temperature fuel cells and electrolyzers. For tackling this problem, numerous advanced electrocatalysts have been proposed and tested in aqueous model systems. There are, however, increasing and evident concerns regarding the value of stability data coming from such studies. Hence, we anticipate that finding new approaches to assess degradation will be a major undertaking in electrocatalysis research in the next years. Specifically, existing differences between fundamental and actual systems have to be addressed first: (a) electrode architecture; (b) electrolyte; (c) reactant and product transport; and (d) operating conditions. In this perspective, we discuss their influence on the stability of electrocatalysts using the challenging oxygen reduction and oxygen evolution reactions as illustrative cases.

Pyrraline formation prevented by sodium chloride encapsulated by binary blends of different starches and gum Arabic in aqueous model systems and cookies

SummaryPyrraline is a common advanced glycation end product that is closely associated with various chronic diseases and frequently found in commonly consumed foods. In this study, pyrraline formation prevented by NaCl encapsulated by binary blends of different starches and gum arabic was investigated. The results show that in aqueous model systems with encapsulated NaCl addition, the reduction in pyrraline varied from 5.4% to 26.7%, with simultaneous decreases in the 3‐deoxyglucosone (3‐DG) concentration, which varied from 13.1% to 41.4%. In cookies with encapsulated NaCl addition, decreases in pyrraline varied from 10.2% to 31.6% accompanied by simultaneous decreases in 3‐DG, which varied from 14.2% to 39.4%. However, NaCl encapsulation had no impact on the browning extent in aqueous model systems and on the basic sensory indicators of the manufactured cookies, including colour and salty taste.

Interaction pattern of histidine, carnosine and histamine with methylglyoxal and other carbonyl compounds

The ability of histidine to scavenge sugar-derived 1,2-dicarbonyl compounds was investigated using aqueous methanolic model systems containing histidine or histamine in the presence of glucose, methylglyoxal, or glyoxal. The samples were prepared either at room temperature (RT) or at 150 °C and analyzed using ESI-qTOF-MS/MS and isotope labeling technique. Replacing glucose with [U-13C6]glucose allowed the identification of glucose carbon atoms incorporated in the products. Various sugar-generated carbonyl compounds ranging in size from C1 to C6 were captured by histidine or histamine. The majority of the fragments incorporated were either C3 or C2 units originating from glyoxal (C2) or methylglyoxal (C3). The ESI-qTOF-MS/MS analysis indicated that histamine could react with either of the two carbonyl carbons of methylglyoxal utilizing the α-amino group and/or the imidazolium moiety. Furthermore, when histidine was added to 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) generating model system, it completely suppressed the formation of PhIP due to scavenging of phenylacetaldehyde.